window.onload = function() {
	if (document.getElementById('add_mass') && document.getElementById('hideForm')) {
		if(window.addEventListener){
			document.getElementById('add_mass').addEventListener("click", showForm, true);
			document.getElementById('hideForm').addEventListener("click", hideForm, true);
		}else if(window.attachEvent){
			document.getElementById('add_mass').attachEvent("onclick", showForm);
			document.getElementById('hideForm').attachEvent("onclick", hideForm);
		}
	}
}
function showForm() {
	document.getElementById('add').style.display = 'block';
	document.getElementById('add_mass').style.display = 'none';
}
function hideForm() {
	document.getElementById('add').style.display = 'none';
	document.getElementById('add_mass').style.display = 'block';
}